What is a condenser?
November 24, 2008
A condenser is a glass lens or lens system located within or below the stage (sub-stage) on compound microscopes. Its basic function is to gather the light coming in from the illuminator and to concentrate that light into a light cone onto the specimen. High-power objective lenses have very tiny diameters and require concentrated light to work properly.
Condensers aid greatly with the bright-field illumination most commonly used with microscopes. Its highly directional and intense light is aimed from beneath the stage through a condenser lens, the specimen, objective lens, and through the eyepiece to the eye.
A basic condenser is fixed in place. A moveable, more precise and more expensive condenser is the Abbe condenser. It usually can be moved vertically, regulating the amount of light from the illuminator. Mounted sub-stage, it often has an adjustable iris-type diaphragm to control the diameter of the beam of light entering the lens system. By changing the size of the iris and moving the lens up or down, the diameter and focal point of the cone of light that goes through the specimen can be controlled. Abbe condensers are most useful at 400x and higher powers.
A condenser’s numerical aperture (measure of a microscope lens’ resolving power) should equal or exceed that of the objective lens. Higher powers will need condensers with higher numerical apertures. Condensers with numerical apertures of 1.2 are typical for use with objectives delivering magnifications of 400x.